Plumbing up DCNF 36's

FiatFunk

FiatFunk

True Classic
Ok so got the engine in last weekend, figuring out wiring, hoses, etc. Plumbing up the fuel system, how much of the original should I keep? Adding an electric fuel pump, is the charcoal trap worth keeping? Check valve? That whole vapour separator apparatus? Is the fitting high on the tank the fuel delivery and one below the fuel return?
Thanks!
 

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I'm a big believer in simplicity. I got rid of everything in the venting system for my dual Webers. I had a supply line going to my electric pump. I deleted the return line and plugged the spigot on the tank for it. I deleted all the tank vent stuff and ran a simple vent hose from one of the two tank vent spigots to a line that exits in the area by the filler neck and capped the other vent spigot on the tank. Many if not most folks here will disagree with my setup but it worked for me and really cleaned up the engine bay.
 
Whatever route you choose to go, do not forget to vent the tank. A fuel pump will easily create enough vacuum to collapse the tank and ruin it. Personally, I followed a similar methodology to Carl, but I left in the original vapor breather, etc.
 
Cool thanks guys, I too like to keep it simple.
The larger diameter pipe above the smaller is the fuel delivery right?
I had a look at the original carb and manifold last night, forgot how small that carb was! Really looking forward to driving this thing.

How about the crankcase vent? Do we just place a filter on that and it vents to atmosphere? And same with the one above it on the head? (Not sure what that is called?)
 
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As Carl notes, simplicity is good. And as Eric suggested, you need to make sure you vent the tank. Here's how I did it on a '74 that has DCNFs on it. Not so simple, but effective.
I did away with the vapor separators and just ran the two vents together using a "T" from the original system to connect them to an old fuel filter so that the air entering the fuel tank (as the gas is pumped out) is filtered. Note - the IN end of the filter is open to the atmosphere. Then I mounted the pump low so that it wasn't trying to suck the gas up hill, and put a pre-filter before the pump. (You might want to consider using some kind of rubber isolators to mount the fuel pump. I didn't and it's pretty noisy.) Next I placed another filter after the pump, kinda belt and suspenders because my fuel tank isn't new.
I didn't use the fuel return nipple because there is no return on the DCNFs like there is on the original DMTR, so it's capped. It hasn't caused me any issues.
I also used the original solenoid for the carb cooling fan to power the fuel pump. And, because there was an extra stud available on the old carb fan mounting bracket I added a start button - because I could. It helps to check valve clearances, etc. (BTW - I have a start solenoid in the starter circuit too.)
20240322_095411.jpg
Yes, the larger nipple is fuel out, the smaller fuel return.
For the engine crankcase vent you can run a hose to a catch can, and then vent the can. Or, you can do what I did and just add a valve cover filter up high above the cyclonic vent.
20240322_102428.jpg
There is no vent on the head. You may be referring to the air injection one way valve that the '79s used. If you no longer have an air pump, remove it and plug the hole.

BTW - it always helps to add the year of your car to your signature. It can help folks help you.
 
For the crankcase vent I ran a long hose from the block to the opening leading into the fuel filler tube area. There was very little blowby in this motor (I guess I did a good job when I rebuilt it).
 
MikeHynes said:
As Carl notes, simplicity is good. And as Eric suggested, you need to make sure you vent the tank. Here's how I did it on a '74 that has DCNFs on it. Not so simple, but effective.
I did away with the vapor separators and just ran the two vents together using a "T" from the original system to connect them to an old fuel filter so that the air entering the fuel tank (as the gas is pumped out) is filtered. Note - the IN end of the filter is open to the atmosphere. Then I mounted the pump low so that it wasn't trying to suck the gas up hill, and put a pre-filter before the pump. (You might want to consider using some kind of rubber isolators to mount the fuel pump. I didn't and it's pretty noisy.) Next I placed another filter after the pump, kinda belt and suspenders because my fuel tank isn't new.
I didn't use the fuel return nipple because there is no return on the DCNFs like there is on the original DMTR, so it's capped. It hasn't caused me any issues.
I also used the original solenoid for the carb cooling fan to power the fuel pump. And, because there was an extra stud available on the old carb fan mounting bracket I added a start button - because I could. It helps to check valve clearances, etc. (BTW - I have a start solenoid in the starter circuit too.)
View attachment 82792
Yes, the larger nipple is fuel out, the smaller fuel return.
For the engine crankcase vent you can run a hose to a catch can, and then vent the can. Or, you can do what I did and just add a valve cover filter up high above the cyclonic vent.
View attachment 82793
There is no vent on the head. You may be referring to the air injection one way valve that the '79s used. If you no longer have an air pump, remove it and plug the hole.

BTW - it always helps to add the year of your car to your signature. It can help folks help you.
Click to expand...
Thanks Mike, helpful pics and advice. What does your start button activate?
This is the vent on the front of the head I was referring too, I believe it was connected to the original air cleaner.
 

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MikeHynes said:
As Carl notes, simplicity is good. And as Eric suggested, you need to make sure you vent the tank. Here's how I did it on a '74 that has DCNFs on it. Not so simple, but effective.
I did away with the vapor separators and just ran the two vents together using a "T" from the original system to connect them to an old fuel filter so that the air entering the fuel tank (as the gas is pumped out) is filtered. Note - the IN end of the filter is open to the atmosphere. Then I mounted the pump low so that it wasn't trying to suck the gas up hill, and put a pre-filter before the pump. (You might want to consider using some kind of rubber isolators to mount the fuel pump. I didn't and it's pretty noisy.) Next I placed another filter after the pump, kinda belt and suspenders because my fuel tank isn't new.
I didn't use the fuel return nipple because there is no return on the DCNFs like there is on the original DMTR, so it's capped. It hasn't caused me any issues.
I also used the original solenoid for the carb cooling fan to power the fuel pump. And, because there was an extra stud available on the old carb fan mounting bracket I added a start button - because I could. It helps to check valve clearances, etc. (BTW - I have a start solenoid in the starter circuit too.)
View attachment 82792
Yes, the larger nipple is fuel out, the smaller fuel return.
For the engine crankcase vent you can run a hose to a catch can, and then vent the can. Or, you can do what I did and just add a valve cover filter up high above the cyclonic vent.
View attachment 82793
There is no vent on the head. You may be referring to the air injection one way valve that the '79s used. If you no longer have an air pump, remove it and plug the hole.

BTW - it always helps to add the year of your car to your signature. It can help folks help you.
Click to expand...
If it is a 74, it should have come with a start button in the engine compartment and a starter relay above the passenger footwell as part of the seat belt interlock system.
 
For my DCNFs, I kept the original vapor separator system as it seemed to be working. Still using the mechanical fuel pump without issue. The charcoal cannister is just vented to open air as opposed to the original hose connected to the exhaust manifold heat shield. For the crankcase vent, it is pretty much stock except that it goes to a fitting on my Sprint Filter filter which covers both DCNFs.
 
FiatFunk said:
Thanks Mike, helpful pics and advice. What does your start button activate?
Click to expand...
The start button activates the starter relay I installed. (It's just behind the "vent filter" in the pic above.) There is constant power wire to the carb cooling fan and since I'm not using the fan I power up the starter solenoid with it through the "start" button.
 
I did away with the charcoal filter as well. Still run the mechanical fuel pump. I added a king fuel filter with regulator and went to an fitting. The crankcase breather has a filter on it. I added a starter relay with remote start button to make it easier to start and adj the carbs by yourself.
20231124_131214.jpg
 
docpan said:
I did away with the charcoal filter as well. Still run the mechanical fuel pump. I added a king fuel filter with regulator and went to an fitting. The crankcase breather has a filter on it. I added a starter relay with remote start button to make it easier to start and adj the carbs by yourself.
View attachment 83383
Click to expand...
nice heat shields!
 
docpan said:
I did away with the charcoal filter as well. Still run the mechanical fuel pump. I added a king fuel filter with regulator and went to an fitting. The crankcase breather has a filter on it. I added a starter relay with remote start button to make it easier to start and adj the carbs by yourself.
View attachment 83383
Click to expand...
Nice job.
Is that a wideband O2 cable I see at the bottom?
 
The heat shields are made from 1/2 inch phenolic board from this seller on ebay Dashman's Hot Rod and Speed Parts. He custom cut them to size. The metal heat shield fits in between the exhaust and intake manifold. Not fasten just wedged in. That is a o2 sensor hooked up to a gauge that hangs on the ash tray. Comes in handy when tuning
 
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